<!DOCTYPE html>

<html>

<head lang="en">
  <meta charset="UTF-8">
  <title></title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    table {
      border-collapse: collapse;
      border-spacing: 0;
      border: 1px solid #c0c0c0;
      width: 500px;
      margin: 100px auto;
      text-align: center;
    }

    th {
      background-color: #09c;
      font: bold 16px "微软雅黑";
      color: #fff;
      height: 35px;
    }

    td {
      border: 1px solid #d0d0d0;
      color: #404060;
      padding: 10px;
    }


    .allCheck {
      width: 80px;
    }
  </style>
</head>

<body>
  <table>
    <tr>
      <th class="allCheck">
        <input type="checkbox" name="" id="checkAll"> <span class="all">全选</span>
      </th>
      <th>商品</th>
      <th>商家</th>
      <th>价格</th>
    </tr>
    <tr>
      <td>
        <input type="checkbox" name="check" class="ck">
      </td>
      <td>小米手机</td>
      <td>小米</td>
      <td>￥1999</td>
    </tr>
    <tr>
      <td>
        <input type="checkbox" name="check" class="ck">
      </td>
      <td>小米净水器</td>
      <td>小米</td>
      <td>￥4999</td>
    </tr>
    <tr>
      <td>
        <input type="checkbox" name="check" class="ck">
      </td>
      <td>小米电视</td>
      <td>小米</td>
      <td>￥5999</td>
    </tr>
  </table>
  <script>
    // ============================== 全选案例 ==============================
    const checkAll = document.querySelector('#checkAll')
    let cks = document.querySelectorAll('.ck')



    // 需求1. 点击全选按钮，下面小按钮跟随变化
      checkAll.addEventListener('click',function(){
        cks.forEach(ele => ele.checked = this.checked)
      })

    // 需求2. 小复选框控制全选按钮
    
   cks.forEach(ele =>{
    //    2.1 给每个小复选框注册 click 事件
    ele.addEventListener('click',function(){
      // 2.2 点击的时候，来判断三个小复选框是否都选中了 ===> 通过every来判断
      checkAll.checked = Array.from(cks).every(e => e.checked === true)
    })
   })
  </script>
</body>

</html>